Turboprop Unit For Aircraft With Improved Aerodynamic Installation

ABSTRACT

A turboprop engine includes a power jet mounted coaxially to the engine axis (X-X′), and has a fan case and a gas ejecting system provided with two afterbody half-cowlings ( 10   b ) each of which is pivotable around an axis (A 2 ) between open and closed positions, wherein the half-cowlings are connected to the downstream of the fan case through a ‘V-blade/V-groove’ system. In a first embodiment, the pivot axes (A 2 ) make an angle α&gt;3° to the engine axis (X, X′) and a joint plane (Z 2 -Z 2 ) between the afterbody half-cowlings and the downstream of the fan case makes to the plane (Y, Y′) perpendicular to the engine axis (X, X′) an angle β in such a way that the difference between the angle α and the angle β is less than or equal to 3°. In the other embodiment, the axes are converged to each other in a downstream direction.

The present invention relates in a general way to a turboprop unit foran aircraft, comprising in particular, from upstream to downstream withrespect to the direction of gas flow, a jet engine having a fan casingand a gas exhaust system, these being coaxial with an engine axis, thesaid gas exhaust system including two afterbody half-cowlings, calledD-ducts, each hinged about an axis, enabling them to move, for thepurposes of maintenance operations, from a closed position to an openposition.

In the closed position, the said afterbody half-cowlings are alsoconnected to the downstream end of the fan casing via a means forsealing and strain transmission, having complementary male and femaleprofiles, called a “V-blade/V-groove” system, the male profile belongingto the afterbody half-cowlings and the female profile belonging to thefan casing side.

In the known art, the downstream outlet plane of the fan casing isstrictly perpendicular to the engine axis, and the hinge axes of thehalf-cowlings are parallel to each other and inclined at an angle α withrespect to the engine axis, this angle not being allowed to exceed 2 to3 degrees, because above this value it would be difficult for the“V-blade/V-groove” system to engage correctly, owing to a “chisel”effect, and, furthermore, the increased friction caused by such adifficult engagement would lead to premature wear.

However, it would be useful to increase this angle α in order to reducethe amount of projection caused by the fairing of the hinges forming thehinge axes of the afterbody half-cowlings. This is because thisprojection complicates the aerodynamic design of the area in question.

The present invention provides a solution enabling the angle α to beincreased while maintaining correct operation of the “V-blade/V-groove”system.

Thus, according to the invention, the angle α formed between the hingeaxes and the engine axis is greater than 3°, and the plane of the jointbetween the afterbody half-cowlings and the downstream end of the fancasing forms an angle β with the plane perpendicular to the engine axissuch that the difference between the angle α and the angle β is lessthan or equal to approximately 3°.

Clearly, this requires a modification of the rear of the jet engine fancasing and of the front of the afterbody half-cowlings carrying thefemale and male components, respectively, of the “V-blade/V-groove”system, but it provides a significant reduction in the projection of theaforesaid hinges.

However, the angles α and β cannot be increased to any value, since anexcessively large angle β would introduce strains not parallel to theengine axis in the engine casing structure, leading to problems ofmechanical strength.

Consequently, the angle α is preferably less than or equal to 6°.

If the jet engine is fitted under a wing, the hinge axes of theafterbody half-cowlings are fixed to a pylon, which is a fairedstructure integrated into the structure of the said wing and, in theknown art, the hinge axes are strictly parallel to each other and to theaxis of the pylon.

To achieve a further reduction in the projection due to the presence ofthe hinges forming these hinge axes, the invention proposes, in additionto the increase in the angle α and in the inclination β of the plane ofthe “V-blade/V-groove” system, or as a variant of these means, theconvergence of the said hinge axes towards each other in the downstreamdirection.

The angle of convergence, with respect to the axis of the pylon, ispreferably about 1°, and therefore the angle between the hinge axes isabout 2°.

The invention will be made clearer by the following description,provided with reference to the attached drawings, in which:

FIG. 1 is an exploded perspective view of the propulsion system of theAirbus A318 engine (underwing nacelle), illustrating the prior art;

FIG. 2 is a diagram of a “V-blade/V-groove” system;

FIG. 3 shows a partial profile view of an underwing nacelle according tothe prior art;

FIG. 4 is a section through the nacelle of FIG. 3, taken in a verticalplane;

FIG. 5 shows a partial profile view of an underwing nacelle according tothe invention;

FIG. 6 is a section through the nacelle of FIG. 5, taken in a verticalplane;

FIG. 7 is a diagram showing, from above, the pylon and the afterbodyhalf-cowlings with their hinge axes; and

FIG. 8 is a schematic section taken in the rear area, showing the effectof the position of the hinge axes on the amount of projection seen inthe fairing due to the presence of the hinges.

In the following description, the same references are used from onefigure to the next to indicate identical or similar parts.

FIG. 1 shows a propulsion system according to the prior art, in whichcan be seen the air intake 1, the fan 2, the fan casing 3, thecompressors 4, the combustion chamber 5, the turbine casing 6, and theexhaust nozzle which is a common exhaust nozzle (for mixed hot and coldgases), generally termed a CNA, standing for “common nozzle assembly”.

The system also includes an engine cowl in two parts, 9 a and 9 b, andan afterbody cowling in two parts, 10 a and 10 b, adapted to surroundthe assembly formed by the compressors 4, the combustion chamber 5 andthe turbine casing 6, the division of the engine cowl and the afterbodycowling into two parts being made along a substantially vertical cuttingplane. Each afterbody half-cowling 10 a, 10 b, generally termed aD-duct, has three aerodynamic surfaces or skins, namely an outer nacellesurface 11, an outer fan channel surface 12 and an inner fan channelsurface 13. The surfaces 12 and 13 delimit half fan channels (cold flow)14 a and 14 b respectively. The CAN 7, which in normal operation isconnected to the afterbody half-cowlings, has two aerodynamic surfaces,namely the outer nacelle surface 15 and the inner surface 16 for themixed hot and cold flow channel. Thrust reverser ports 17 are fitted inthe cowling 10 a, 10 b to act on the cold flow.

The engine cowl and the afterbody cowling are each formed from twohalves 9 a, 9 b and 10 a, 10 b respectively, but the common nozzle orCNA 7 is made in one piece. The half-cowls 9 a and 9 b and thehalf-cowlings 10 a and 10 b are fitted by hinging on the engine beam(not shown) by means of the hinges 18 and 19 respectively. At theopposite ends from the hinges, the half-cowls 9 a, 9 b and thehalf-cowlings 10 a, 10 b have locks such as 20 and 21, enabling them tobe locked in the closed position. Clearly, the purpose of this fittingin two hinged parts is to allow easier access to the cold and hot partsof the jet engine.

The afterbody half-cowling 10 a, 10 b is fixed to the engine by means ofstructures called V-blade/V-groove, whose position on the upstream endof the half-cowling 10 b is shown at 22, for connection to the fancasing 3. Complementary structures such as 23 (FIG. 2) are placed in afacing position on the said casing.

The joint plane Z-Z′ (Z₁-Z₁′ in FIG. 4) of the “V-blade/V-groove” systemcoincides with a plane Y-Y′ perpendicular to the engine axis X-X′, sothat the angle β₁ (FIG. 4) between the two planes is zero.

A similar “V-blade/V-groove” system is provided between the downstreamedge of the half-cowlings 10 a, 10 b and the upstream edge of the CNA 7,and, in this case also, the joint plane of the “V-blade/V-groove” systemcoincides with a plane perpendicular to the engine axis X-X′.

FIG. 3 shows a nacelle 24 fitted to a pylon 25 extending from the wing26 of an aircraft. As shown, an area indicated by 27, of length L,projects from the overall profile of the nacelle 24. This is due to thepresence of the fairing of the hinges 19, which are positioned along ahinge axis A1 (FIG. 4) which forms an angle α₁<3° with the engine axisX-X′.

According to the invention, this angle is increased to α₂>3, in such away that the hinge axis now occupies the position A₂ and simultaneouslyan angle β₂ is created between the joint plane of the “V-blade/V-groove”system, which thus becomes Z₂-Z₂′, and the plane Y-Y′.

This angle β₂ is such that α₂−β₂≦3

As shown in FIGS. 5 and 6, this produces a very significant reduction inthe projection, which becomes 27′, as regards both the length, whichchanges from L to 1, and the height.

Clearly, the joint plane of the “V-blade/V-groove” system between thedownstream edge of the afterbody half-cowlings 10 a, 10 b and theupstream edge of the CNA 7 must, according to the invention, be inclinedat an angle β₂ with respect to the plane perpendicular to the engineaxis X-X′, as must the joint plane of the “V-blade/V-groove” systembetween the upstream edge of the half-cowlings 10 a, 10 b and thedownstream edge of the fan casing 3.

The projection can be reduced further by taking another step shown inFIGS. 7 and 8.

FIG. 7 shows schematically the pylon 25 and the two afterbodyhalf-cowlings 10 a, 10 b with their hinge axes.

In the prior art, the hinge axes occupy the position A1; in other words,they are parallel to each other and to the longitudinal axis P-P′ of thepylon 25. This position corresponds to the projection shown at 27 inFIGS. 3, 4 and 8.

However, if these axes are made to converge slightly towards the rear ordownstream end, at an angle δ with respect to the axis P-P′, thus movingthem to A₃, there is a marked reduction in the projection, shown at 27″in FIG. 8.

Thus by combining these two steps (greater inclination of the hinge axeswith respect to the engine axis, with appropriate inclination of thejoint plane of the “V-blade/V-groove” system, on the one hand, andconvergence of the hinge axes with respect to the axis of the pylon, onthe other hand) it is possible to achieve a substantial reduction of theprojection size, which is beneficial in terms of the aerodynamic designof the nacelle/pylon/wing area.

Although the invention has been described mainly in relation to a longmixed-flow nacelle, it is also clearly applicable to a shortseparate-flow nacelle. Similarly, although the invention has beendescribed in application to an “underwing engine” configuration, it isapplicable to what is known as a “fuselage side mounted engine”. Itshould also be noted that the invention is equally applicable both toafterbodies incorporating thrust reverser doors, as described withreference to FIG. 1, and to afterbodies without these doors.

1-5. (canceled)
 6. A turboprop unit for an aircraft, comprising inparticular, from upstream to downstream with respect to the direction ofgas flow, a jet engine having a fan casing and a gas exhaust system,these being coaxial with an engine axis, the said gas exhaust systemincluding two afterbody half-cowlings, each hinged about an axis,enabling them to move from an open maintenance position to a closedposition in which the said afterbody half-cowlings are also connected tothe downstream end of the said fan casing via a means for sealing andstrain transmission, called a “V-blade/V-groove” system, the said hingeaxes forming an angle α with the engine axis, wherein this angle α isgreater than 3° and the joint plane between the said afterbodyhalf-cowlings and the said downstream end of the said fan casing formsan angle β with the plane perpendicular to the engine axis such that thedifference between the angle α and the angle β is less than or equal to3°.
 7. The turboprop unit as claimed in claim 6, wherein the angle α isless than or equal to 6°.
 8. The turboprop unit as claimed in claim 6,mounted under a wing, in which the said hinge axes are fixed to a pylonintegrated in the structure of the said wing, wherein the said hingeaxes converge towards each other in the downstream direction.
 9. Theturboprop unit as claimed in claim 6, mounted under a wing, in which thesaid hinge axes are fixed to a pylon integrated in the structure of thesaid wing, wherein the said hinge axes converge towards each other inthe downstream direction, the angle of convergence with respect to theaxis of the pylon being about 1°.
 10. The turboprop unit for anaircraft, comprising in particular, from upstream to downstream withrespect to the direction of gas flow, a jet engine provided with a fancasing and a gas exhaust system, these being coaxial with an engineaxis, the said gas exhaust system including two afterbody half-cowlings,each hinged about an axis, enabling them to move from an openmaintenance position to a closed position in which the said afterbodyhalf-cowlings are also connected to the downstream end of the said fancasing via a means for sealing and strain transmission, called a“V-blade/V-groove” system, the said hinge axes being fixed to a pylonintegrated in the structure of the said wing, wherein the said hingeaxes converge towards each other in the downstream direction.
 11. Theturboprop unit as claimed in claim 10, wherein the angle of convergenceδ with respect to the axis of the pylon is about 1°.